This patch implements the FIEMAP ioctl for GFS2. We can use the genericcode (aside from a lock order issue, solved as per Ted Tso's suggestion)for which I've introduced a new variant of the generic function. We alsohave one exception to deal with, namely stuffed files, so we do that"by hand", setting all the required flags.

This has been tested with a modified (I could only find an old version) ofEric's test program, and appears to work correctly.

This patch does not currently support FIEMAP of xattrs, but the plan is to addthat feature at some future point.